Consistent with its effects on AF inducibility, apelin administration resulted in prolongation (P = 0.0004) of the atrial effective refractory period by approximately 16% (Figure 2F) in the atria of exercised mice, an effect that was also observed in control sedentary mice (~11% increase, P < 0.0001, n = 6). This evidence concerns the gene APLN and atrial fibrillation.